This invention relates generally to seismic isolation bearings, and more particularly to a seismic isolation device providing an articulating joint.
Many inhabited areas are subject to earthquakes and other seismic activity. Building designs have been developed to limit the property damage, injury, and death due to earthquakes. One approach is to make buildings in seismic areas strong enough to withstand the greatest anticipated strain. Unfortunately, this approach can greatly increase both the material cost and construction cost of the building, and result in a very heavy building. A heavy building can further complicate matters if the building must be placed on a soft or meta-stable ground, like mud or fill. While such ground provides adequate support for the building during normal times, the meta-stable ground may provide reduced support during an earthquake, resulting in the foundation or a portion of the foundation sinking or tilting.
Other approaches have focused on isolating the building (structure) from the foundation and underlying soil that the building rests on. For example, techniques have been developed to allow a structure to slide relative to its foundation. Some devices include a joint with a sliding foot that allows a building to remain vertical as the foot slides. Unfortunately, while a sliding joint may avoid catastrophic failure of the building superstructure, after an earthquake the building may no longer be on its foundation, or the foundation may no longer be level. Other techniques provide an elastomeric bearing that allows some degree of elastic movement between the structure and the foundation. Elastomeric techniques typically focus on allowing shear deformation, that is, the relative movement of the building and foundation in a horizontal plane in response to an earthquake.
One approach to using elastic bearings provides a laminated structure of elastomeric material, such as rubber, interleaved with metal shims. The laminate structure confines the elastomer layers to limit horizontal expansion due to vertical load stresses while allowing shear deformation of the laminate stack in the result of an earthquake. Such laminates do not provide significant compliance for vertical strain, such as may accompany surface waves or tilting, and generally require a high degree of shear deformation, which generally means using an elastomeric material with a high degree of elasticity and/or many laminations.
Therefore, it is desirable to provide seismic isolation between a building and a foundation with improved compliance, including compliance in the vertical plane and tilting. It is further desirable that the seismic isolation be compatible with buildings built on meta-stable ground.